Automatic tolerance inspection through Reverse Engineering: a segmentation technique for plastic injection moulded parts

This work studies segmentations procedures to recognise features in a Reverse Engineering (RE) application that is oriented to computer-aided tolerance inspection of injection moulding die set-up, necessary to manufacture electromechanical components. It will discuss all steps of the procedures, from the initial acquisition to the final measure data management, but specific original developments will be focused on the RE post-processing method, that should solve the problem related to the automation of the surface recognition and then of the inspection process. As it will be explained in the first two Chapters, automation of the inspection process pertains, eminently, to feature recognition after the segmentation process. This work presents a voxel-based approach with the aim of reducing the computation efforts related to tessellation and curvature analysis, with or without filtering. In fact, a voxel structure approximates the shape through parallelepipeds that include small sub-set of points. In this sense, it represents a filter, since the number of voxels is less than the total number of points, but also a local approximation of the surface, if proper fitting models are applied. Through sensitivity analysis and industrial applications, limits and perspectives of the proposed algorithms are discussed and validated in terms of accuracy and save of time. Validation case-studies are taken from real applications made in ABB Sace S.p.A., that promoted this research. Plastic injection moulding of electromechanical components has a time-consuming die set-up. It is due to the necessity of providing dies with many cavities, which during the cooling phase may present different stamping conditions, thus defects that include lengths outside their dimensional tolerance, and geometrical errors. To increase the industrial efficiency, the automation of the inspection is not only due to the automatic recognition of features but also to a computer-aided inspection protocol (path planning and inspection data management). For this reason, also these steps will be faced, as the natural framework of the thesis research activity. The work structure concerns with six chapters. In Chapter 1, an introduction to the whole procedure is presented, focusing on reasons and utilities of the application of RE techniques in industrial engineering. Chapter 2 analyses acquisition issues and methods that are related to our application, describing: (a) selected hardware; (b) adopted strategy related to the cloud of point acquisition. In Chapter 3, the proposed RE post-processing is described together with a state of art about data segmentation and surface reconstruction. Chapter 4 discusses the proposed algorithms through sensitivity studies concerning thresholds and parameters utilised in segmentation phase and surface reconstruction. Chapter 5 explains briefly the inspection workflow, PDM requirements and solution, together with a preliminary assessing of measures and their reliability. These three chapters (3, 4 and 5) report final sections, called “Discussion”, in which specific considerations are given. Finally, Chapter 6 gives examples of the proposed segmentation technique in the framework of the industrial applications, through specific case studies

Three-dimensional object reconstruction from two-dimensional images

In order to construct a 3D model from a collection of 2D images of an object, an energy function is defined between the object's images and corresponding images ofan articulated mesh in three dimensions. Repeated adjustment of the mesh to minimize the energy function results in a mesh that produces images which closelyapproximate the input images, that is to say that under the appropriate conditions it realizes a preconceived object. It has implications for model building, reverseengineering and computer vision. Minimization of the energy function is a multivariate problem of large scale with many local minima. We give an approach forsolving this problem. For certain restricted, but useful applications, intuitive solutions to the minimization are consistently obtained

Interdisziplinäre Kooperation bei der Erstellung virtueller geschichtswissenschaftlicher 3D-Rekonstruktionen

Virtuelle 3D-Modelle finden in den historischen Disziplinen in zweierlei Art Verwendung. Zum einen dienen diese zur Erfassung und Digitalisierung existierender historischer Objekte. Daneben dient die Erstellung von virtuellen 3D-Rekonstruktionen der Nachbildung nicht mehr existierender Objekte und Strukturen. Während technische Abläufe beider Ansätze ebenso wie methodische und wissenschaftstheoretische Aspekte in der Fachliteratur häufig und umfassend thematisiert werden, ist eine Frage nach sozialen Aspekten und sozialer Interaktion im Kontext derartiger Vorhaben bisher unbeleuchtet geblieben. Ziel der Arbeit stellt dar, eine Bandbreite und Relevanz von Aspekten der Kooperation als „Zusammenarbeit mit gemeinsamem Ziel, gegenseitiger Abstimmung, planvollem Vorgehen sowie Vorteilen für alle Akteure“ (Hagenhoff, 2004) im Kontext derartiger geschichtswissenschaftlicher 3D-Modellierungsvorhaben mittels sozialwissenschaftlicher Methoden zu beleuchten. Dabei zielt eine Darlegung auf unterschiedliche Skalierungen von Kooperation ab – angefangen bei einer Wissenschaftslandschaft über Kooperationsstrukturen bis hin zu einer Betrachtung von spezifischen Kooperationsphänomenen und -strategien innerhalb von Arbeits- und Erstellungsprozessen